What is the appropriate azithromycin dosage for a 6‑year‑old child weighing 48 lb (≈21.8 kg)?

Azithromycin Dosing for a 6-Year-Old Weighing 48 Pounds

For a 6-year-old child weighing 48 pounds (21.8 kg), the appropriate azithromycin dose is 200 mg once daily, based on weight-band dosing guidelines from the British Thoracic Society. 1

Weight-Based Dosing Algorithm

Your patient falls into the 15–25 kg weight band (48 lb = 21.8 kg), which corresponds to 200 mg once daily 1, 2. This dosing is derived from the standard pediatric calculation of 10 mg/kg once daily (maximum 500 mg per dose) 1, 3.

Dosing by Weight Band (6 months–17 years):

• 15–25 kg: 200 mg once daily 1, 2
• 26–35 kg: 300 mg once daily 1, 2
• 36–45 kg: 400 mg once daily 1, 2
• ≥46 kg: 500 mg once daily 1, 2

Indication-Specific Regimens

The dosing schedule varies by indication:

Community-Acquired Pneumonia (Atypical Pathogens)

10 mg/kg (max 500 mg) on Day 1, then 5 mg/kg (max 250 mg) daily for Days 2–5 2, 3. For your 21.8 kg patient, this translates to approximately 220 mg Day 1, then 110 mg Days 2–5. However, the practical weight-band approach simplifies this to 200 mg Day 1, then 100 mg Days 2–5 using available suspension formulations 2.

Critical caveat: Azithromycin is appropriate only for atypical pathogens (Mycoplasma pneumoniae, Chlamydia pneumoniae, Chlamydia trachomatis) 2. For typical bacterial pneumonia caused by Streptococcus pneumoniae or Haemophilus influenzae, amoxicillin at 90 mg/kg/day remains first-line therapy; azithromycin should not be used as monotherapy 2.

Acute Otitis Media

The FDA label provides three options 3:

• 5-day regimen: 10 mg/kg Day 1, then 5 mg/kg Days 2–5 (≈200 mg Day 1, then 100 mg Days 2–5)
• 3-day regimen: 10 mg/kg once daily for 3 days (≈200 mg daily × 3 days)
• 1-day regimen: 30 mg/kg as a single dose (≈650 mg single dose)

Streptococcal Pharyngitis/Tonsillitis

Azithromycin is second-line therapy only; penicillin or amoxicillin remains first-line 2. If used, the dose is 12 mg/kg once daily for 5 days (≈260 mg daily for 5 days) due to high recurrence rates with standard 10 mg/kg dosing 2, 3, 4.

Acute Bacterial Sinusitis

10 mg/kg once daily for 3 days (≈200 mg daily × 3 days) 3.

Administration Guidelines

• Can be taken with or without food 3
• Do NOT administer simultaneously with aluminum- or magnesium-containing antacids; separate by at least 2 hours, as antacids reduce drug absorption 1, 2
• Pediatric oral suspension is the preferred formulation for children who cannot swallow tablets 2

Monitoring Requirements

For prolonged courses (e.g., non-tuberculous mycobacterial infections), the British Thoracic Society recommends 1:

• Baseline ECG, repeat at 2 weeks, and after adding any QT-prolonging medications (azithromycin can prolong QT interval)
• Baseline and intermittent audiometry during treatment
• Liver function tests, renal function, and complete blood count checked sporadically throughout treatment

For standard short-course respiratory infections, routine monitoring is generally not required 2.

Expected Clinical Response

Children should demonstrate clinical improvement within 48–72 hours 2. If no improvement or clinical deterioration occurs within this timeframe, reassess the diagnosis, consider alternative pathogens (including resistance patterns or complications), and adjust therapy accordingly 2.

Common Pitfalls to Avoid

1. Do not underdose the initial Day 1 dose; full 10 mg/kg dosing is essential to achieve therapeutic tissue levels 2
2. Do not prescribe azithromycin as first-line for typical bacterial pneumonia or streptococcal pharyngitis, as β-lactam agents have superior outcomes and lower recurrence rates 2
3. Verify suspension concentration (100 mg/5 mL vs 200 mg/5 mL) before calculating volume to avoid dosing errors 2, 3
4. Azithromycin is not appropriate for most upper respiratory tract infections (URTIs), as the vast majority are viral and do not benefit from antibiotics 5

Adverse Effects

Common adverse effects include gastrointestinal disturbances (abdominal discomfort, diarrhea, nausea, vomiting), dizziness, and headache 1, 2. Azithromycin has significantly fewer gastrointestinal side effects compared to erythromycin 2, 4, 6. Rare but serious adverse effects include acute interstitial nephritis, allergic reactions/anaphylaxis, and pseudomembranous colitis 2.